1. Field of the Invention 
The present invention relates generally to printer ribbons and, more particularly, to a detectable spool including indicia that indicate properties of a length of ribbon wound on the detectable spool. 
2. Description of the Related Art 
Thermal transfer printing equipment is generally known in the relevant art. One type of known thermal transfer process involves the application with a thermal print head of an elevated temperature to regions of a thermal transfer ribbon, with resultant melting of an ink compound of the ribbon at the aforementioned regions. The molten ink compound becomes transferred onto a substrate, which thereby imprints the ink compound onto the substrate. Each ribbon typically is divided into a plurality of consecutively positioned panels, with each panel being usable only for a single printing operation. 
Depending upon the type of printing being performed, it may be desirable to have different types of panels provided on the same ribbon. For instance, when it is desired to perform color printing, a given ribbon may consecutively include separate panels containing ink compounds that are colored yellow, magenta, and cyan. A color  image that is desired to be printed onto a substrate may be broken up into component images of yellow, magenta, and cyan light. A single color printing operation thus may include three consecutive printing operations, one involving yellow ink, one involving magenta ink, and one involving cyan ink. An appropriately configured color thermal transfer ribbon thus might include consecutive yellow, magenta, and cyan panels repetitively from the beginning of the ribbon to the end of the ribbon. Such a ribbon might bear a designation such as YMC to designate the yellow/magenta/cyan repetitive pattern. 
It may additionally be desirable for each series of color panels on the ribbon to be followed by a black panel if it is desired that black printing be provided along with color printing. Such a black panel may be designated by the letter K in the ribbon designation. It may further be desirable to provide an overlay panel on the ribbon which can be used to apply a scratch-resistant overlay surface to the substrate after color and/or black imprintation has occurred. Such an overlay panel may be designated by the letter O in the ribbon designation. It can be seen, therefore, that a thermal transfer ribbon having repetitive series of yellow, magenta, cyan, black, and overlay panels would bear the designation YMCKO. It similarly can be seen that a thermal transfer ribbon having repetitive panels solely of black ink would bear the designation K. 
It thus can be seen that numerous different ribbon configurations are possible. It can further be seen that the large number of different ribbon configurations can potentially cause a ribbon having a given panel configuration to be confused by a technician or operator with another ribbon having a different panel configuration. It has thus been deemed desirable to provide some type of indicia on a ribbon spool that will identify to a printer the specific panel configuration of the ribbon wound on the spool. Such a system is the subject of U.S. Pat. No. 5,755,519 to Klinefelter and U.S. Pat. No. 6,152,625 to Oliverio. It is desired, however, to provide an improved detectable spool with identifier indicia that are more reliable, both structurally and  operationally, and that can be manufactured less expensively than previously known detectable spools. It is also desired to provide such an improved detectable spool that additionally includes identifier indicia that can visually indicate to an observer the specific panel arrangement of a ribbon. 